T-Pain Is On A Boat: [Electric Boats] Re: motor overheating

Thursday, July 2, 2009

[Electric Boats] Re: motor overheating

[Sorry if this is a dupe - groups keeps losing posts]

I had a chance to test this today. ~15kt winds, 1' chop. I ran the boat downwind (no sails) at 40amps, got to 4.4kts. Turned 180 into the wind, and amp draw increased to 47amps, boatspeed dropped to 2.2kts. I ran in both directions long enough for a steady read.

Similarly, I've seen amps drop when motorsailing and the wind comes up, but that's harder to measure (the ultimate form of that being [weak] regen)

-Keith

--- In electricboats@yahoogroups.com, "dennis wolfe" <dwolfe@...> wrote:
>
> Keith,
>
> Slip does increase as the headwind (or any extra resistance increases) increases. Water is 'sorta' squishy ( not really compressible but flows 'sorts' easily) The 'sorta' is why amp draw goes up.
>
> With increases resistance the amps go up AND the boat slows down. The slowing down is why the amps go up - because the slip increases. The work the motor does is based on accelerating a mass of water backwards. The faster the boat is going forward, the less the prop can accelerate it backwards - hence less work, less amps.
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> Next time you are out in your famous windy bay try WOT upwind and downwind and let us know the results. Up wind will be more.
>
> Denny
>
> ----- Original Message -----
> From: aweekdaysailor
> To: electricboats@yahoogroups.com
> Sent: Tuesday, June 23, 2009 12:26 AM
> Subject: [Electric Boats] Re: motor overheating
>
>
>
>
>
> Thanks Denny,
>
> So tied to the dock, slip is 100%. Pushing into a headwind - doesn't slip increase as well? Based on experience and intuition the boat just slows down - amps stays constant at a given throttle. You have to up throttle (voltage) to compensate and try to maintain speed.
>
> If we were talking golf carts again, I'd buy into the amps increasing. But water is squishy and will follow the path of least resistance - and given enough wind that would be sideways.
>
> But I'll do some homework to make sure I'm not just talking through my hat.
>
> -Keith
>
> (and I'm wondering if I've got a problem in my motor or ammeter - I can pull 20amps at WOT no load, belt removed)
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